1. Field of the Invention
This invention relates to safe-arm initiators for explosive devices, and more particularly to firing-type explosive initiators incorporating electromechanical safing and arming means. Still more particularly, it is concerned with a remotely operated initiator of the class described which, when either safed or armed, can be relied on to remain in that state unless and until commanded to assume the alternate status, even in the event of a control power failure.
2. Prior Art
Explosive initiators having internal firing means and integrated safe-arm capacity are well known. The safing and arming mechanisms employed in these devices take a variety of forms, but they are all designed to prevent or effectively impede the propagating of the output of the initiator's primary charge to the explosive train. The basic design criteria for the safe-arm mechanism are dictated to a great extent by the characteristics of the primary pyrotechnics charge used in the initiator.
The overwhelming majority of the "explosive cartridges" employed to achieve initial reaction in explosive initiators are in reality pressure charges. The propellant in a pressure cartridge burns at a relatively low velocity of up to about 400 meters per second, and although the velocity increases with pressure, it can be controlled. Of major concern when designing safe and arm devices using this class of pyrotechnic materials are the requirements for flame travel restriction and pressure containment. Typically, such devices employ specially constructed sealed enclosures, fixed mechanical barriers, and through-bulkhead actuators in their safing and arming designs.
In a true detonation reaction on the other hand, extremely rapid burning of the explosive material produces a supersonic shock, or detonating, wave in the explosive substrate. The detonating velocity in such materials is usually between 2,000 and 9,000 meters per second and is substantially unaffected by pressure. Commonly in such devices, detonation energy is transferred from the detonator to the end of an explosive transfer line by the physical impact of shrapnel. Small particles, expelled from the end of the detonator cartridge at supersonic velocity, impact the end of the transfer line producing a shock wave and subsequent detonation of the explosive train. Safe and arm designs for initiators using this type of pyrotechnic material are principally concerned with the relative geometry between the detonating charge and the pick-up component. Heat and pressure containment is of little significance. The subject invention is directed primarily, though not exclusively, to initiators of this class.
The prior art is replete with safing and arming mechanisms for such initiators. Generally, they employ an assembly including moveable components for mechanically disrupting or blocking the propagation path downstream of the initiating charge. Typically, a more or less conventional electromechanical solenoid or relay, in combination with appropriate switches, ratchets, linkages, levers, cams, clutches, springs, and the like, selectively positions the moveable components to achieve the safe or armed condition.
These prior art safe-arm mechanisms suffer from several deficiencies. For one, since by their nature, solenoids and relays are capable of only limited, unidirectional motion, the control they can exert over the movement of the initiator's components is limited. For another, these devices and their accessories tend to be relatively bulky and heavy. Some are so elaborate that initiators incorporating them require specially augmented detonators or booster charges simply to assure bridging of the explosive transfer gap. For still another, not unexpectedly, their complexity imposes a high price on their manufacture and maintenance, and an even higher one on their reliability.
To afford some of the utilities inherent in the larger, more complex safe-arm systems in a more compact, less elaborate device, initiators of the type disclosed in U.S. Pat. No. 3,500,747 have been developed. These employ electromagnets to cause rotation of an out-of-line ignition bead or primary charge housed within a barrel-like rotor into alignment with an explosive output charge. While electromagnetically operated initiators of this type offer a number of advantages, heretofore their use has been limited by their lack of suitable means for reliably retaining the charge-bearing rotor in the safe and armed positions.
Commonly in such devices, the torque generated by a pair of opposed electromagnets is employed to hold the rotor against a mechanical stop and thereby both position and retain the charge. Continuous operation of an electromagnet under a load, however, consumes power and generates heat. Adapting this type of electromagnetic control for use in arm and fire systems poses significant power consumption and heat dissipation problems.
For many applications, such as missile launching, and ordnance fire control, it is desirable, if not essential, that the initiator's safing and arming mechanism be designed to remain in, or return itself to, the safe condition in the event of a loss of arming power. Such fail-safe devices are well known and in common use. For other applications, however, for example, solid rocket motor thrust termination and vehicle destruction in conjunction with space launch boosters, ballistic missiles, remotely piloted target aircraft, and the like, it is equally important to provide a firing mechanism which will remain armed and operational in the event of the loss of control power. Conventional fail-safe devices are neither designed, nor readily adaptable, to satisfy this requirement. In the case of those employing driving means, such as return springs, pressure accumulators, or the like, for returning components to the safe condition in the event of a loss of power, the provision of an override feature would defeat the very purpose of the fail-safe mechanism. Devices of the type exemplified by U.S. Pat. No. 3,500,747, which depend on the torque generated by an electromagnet to position and retain the critical components, cannot be relied on to remain in the safe or armed condition in the event of a control power failure.
One of the objects of the invention is to provide an electromagnetically operated safe-arm firing type explosive initiator, which affords the advantages, and overcomes the deficiencies, inherent in the prior art safe-arm devices.
Another object is to provide an electromechanical explosive initiator of the type described, which can be repeatedly selectively driven to the safe and armed positions and which will remain stable in either position in the event the electrical driving power fails.
Yet another object is to provide a safe-arm firing initiator which utilizes a rotatable body, rather than pivoting or translating means, to establish and interrupt the explosive transfer path between an internal detonator and an external explosive transfer line.
A more particular object is to provide a device of this type, which does not rely on driving the rotatable body hard over against a mechanical stop for maintaining the device in the safe or armed condition.
Still another object is to provide a safe-arm initiator incorporating an electromagnetically controlled rotatable body, which includes resilient detent means for precisely positioning and reliably retaining the rotatable body in both the safe and armed positions.
A further object is to provide a safe-arm firing initiator of the rotatable body type which is highly resistant to operationally encountered vibration and shock.
A still further object is to provide a remotely operable safe-arm initiator having a manually operable safing mechanism for reliably overriding the arm command and securing the device in the safe condition.
An additional object is to provide in an initiator having manual safing means a visual indicator for reliably determining the condition of the safe-arm mechanism.
Yet a further object is to provide a safe-arm initiator satisfying all of the foregoing objects that is comparatively inexpensive to manufacture and requires no maintenance or repair in the field.
Other objects will become apparent from the following summary of the invention and detailed description of its preferred embodiment.